The present invention relates to a thermally-assisted recording and/or reproducing device, and more particularly, to an improved and novel thermally-assisted recording device capable of heating a magnetic or other kinds of recording media by electron beams to write and/or read data to the medium with an extremely high density.
Personal computer (PC) systems and audio and/or video (AV) systems require a peripheral storage unit which has a large capacity and also is inexpensive. Currently, most of such peripheral storage units are magnetic or optical recording devices. The magnetic recording devices include a fixed magnetic hard disc drive (HDD) and magnetic tape recording device. Many of the PC systems adopt an HDD and an optical disc drive or magnetic tape recording device. Generally, various data including OS (operating system) and other software are stored in the HDD to which random access is made, while the optical disc drive or magnetic tape recording device is used for long-term storage of important data. Conventionally, the AV systems for storage of a large amount of moving picture information use mainly the magnetic tape recording device as the peripheral storage unit. With the larger capacity of the recent HDD and optical recording device, however, it has become expected that the HDD and optical recording device are employed in the AV systems for their speedy accessibility which is not possible with the conventional magnetic tape recording device. The magnetic and optical recording devices for use in the PC systems and AV systems are required to have a larger capacity and higher speed and be more inexpensive. With the conventional peripheral storage units, however, it is said that problems will arise as in the following.
First, the magnetic recording device will be considered. The magnetic recording device to magnetically write and read information has constantly been evolved as a large capacity, high speed and inexpensive information storage means. Among others, the recent hard disc drive (HDD) has shown remarkable improvements. Specifically, as proved on the product level, its recording density is over 10 Gbpsi (gigabits per square inch), internal data transfer rate is over 100 Mbps (megabits per second) and price is as low as several yens/MB (megabytes). The high recording density of HDD is due to a combination of improvements of a plurality of elements such as signal processing technique, servo control mechanisms, head, medium, HID, etc. Recently, however, it has become apparent that the thermal agitation of the medium inhibits the higher density of HDD.
The high density of magnetic recording can be attained by making smaller the recording cell (recording bit) size. However, as the recording cell is made smaller, the signal magnetic field intensity from the medium is reduced. So, to assure a predetermined signal-to-noise ratio (S/N ratio), it is indispensable to reduce the medium noise. The medium noise is caused mainly by a disordered magnetic transition. The magnitude of the disorder is proportional to a magnetic transition unit of the medium. The magnetic medium uses a layer formed from polycrystalline particles (will be referred to as xe2x80x9cmultiparticle layerxe2x80x9d or xe2x80x9cmultiparticle mediumxe2x80x9d herein). In case a magnetic exchange interaction works between magnetic particles, the magnetic transition unit of the multiparticle layer is composed of a plurality of exchange-coupled magnetic particles.
Heretofore, when a medium is to have the recording density is several hundreds Mbpsi to several Gbpsi for example, the lower noise of the medium has been attained mainly by reducing the exchange interaction between the magnetic particles and making smaller the magnetic transition unit. In the latest magnetic medium of 10 Gbpsi in recording density, the magnetic transition unit is of only 2 or 3 magnetic particles. Thus, predictably, the magnetic transition unit will be reduced to only one magnetic particle in near future.
Therefore, to assure a predetermined S/N ratio by further reducing the magnetic transition unit, it is necessary to make smaller the size of the magnetic particles. Taking the volume of a magnetic particle as V, a magnetic energy the particle has can be expressed as KuV where Ku is an anisotropy energy density the particle has. When V is made smaller for a lower medium noise, KuV becomes smaller with a result that the thermal energy each particle has at a temperature near the room temperature will disturb information written in the medium, which is the xe2x80x9cthermal agitationxe2x80x9d referred to herein and has become the problem as mentioned above.
According to the analysis made by Sharrock et al., the ratio between magnetic energy and thermal energy of a particle, KuV/kT where k is Boltzman""s constant and t is absolute temperature, is required to be greater than 100 or so in order to keep the reliability of the record life. If the particle size is decreased for a lower medium noise with the anisotropy energy density Ku being maintained at (2 to 3)xc3x97106 erg/cc of the CoCr group alloy conventionally used as a magnetic layer in the recording medium, it will be difficult to assure a thermal agitation resistance.
More specifically, the multiparticle layer of Co, Cr, Ta and Pt used in the current magnetic recording medium has a Ku value of about (2 to 4)xc3x97106 erg/cc. With a particle size of 10 nmxcfx86-10 nmt or so, the magnetic energy of each particle will be under 100 times of the thermal energy each particle has at the room temperature and there will take place a noticeable destruction of written information due to the thermal agitation. Improvement of the medium material and increasing the anisotropy energy density Ku may look like an approach to the solution of the problem, but a larger value of Ku will be accompanied by a larger coercive force, which will make the information writing to the medium more difficult.
Recently, magnetic layer materials having a Ku value of more than 107 erg/cc such as CoPt, FePd, etc. have been attracting much attention from all the field of industries concerned. However, simply increasing the Ku value for compatibility between the small particle size and thermal agitation resistance will lead to another problem. The problem concerns the recording sensitivity. Specifically, as the Ku value of the magnetic layer of a medium is increased, the recording coercive force Hc0 of the medium (Hc0=Ku/Isb; Isb is a net magnetization of the magnetic layer of the medium) will increase and the necessary magnetic field for saturation recording increase proportionally to Hc0.
A recording magnetic field developed by a recording head and applied to the medium depends upon a current supplied to a recording coil as well as upon a recording magnetic pole material, magnetic pole shape, spacing, medium type, layer thickness, etc. Since the tip of the recording magnetic pole is reduced in size as the recording density is higher, however, the magnetic field developed by the recording head is limited in intensity.
Even a combination of a single-pole head which will develop a largest magnetic field and a vertical medium backed with a soft magnetic material for example can develop a magnetic field whose largest possible intensity is on the order of 10 kOe (Oe: oersted). On the other hand, to assure a sufficient thermal agitation resistance with a necessary particle size of about 5 nm for a future high-density, low-noise medium, it is necessary to use a magnetic layer material having a KU value of 107 erg/cc or more. In this case, however, since the magnetic field intensity necessary for write to the medium at a temperature approximate to the room temperature is over 10 kOe, no write to the medium is possible. Therefore, if the Ku value of the medium is simply increased, there will arise a problem of the write to the medium being impossible.
As having been described in the foregoing, in the magnetic recording using the conventional multiparticle medium, the lower noise, thermal agitation resistance and higher recording density are in a trade-off relation with each other, which is an essential factor upon which the limit of the recording density depends.
Secondly, the optical recording device will be considered. A high density of the optical recording basically depends upon the reduction of the size of a laser spot focused on an optical recording medium. Therefore, for a higher recording density with the optical recording device, a laser light used should be of a shorter wavelength or an objective lens used should have a higher numerical aperture (NA). However, use of a laser light having a shorter wavelength is limited by selection of a laser element material for use with the laser light and also by the spectral transmittances of the substrate of an optical disc and various optical elements included in the optical system of the optical recording device. Recently, there has been proposed a ultrahigh density optical recording using a near-field light (evanescent wave). For practical use of the near-field light, however, there are many problems to solve since the light spot size and light intensity on the medium are theoretically in a trade-off relation with each other.
Therefore, it is predicable that in organizing a future peripheral storage unit having a recording density of over Tb (terabits)/inch2, both the conventional magnetic and optical recording systems will encounter many difficulties.
Accordingly, the present invention has an object to overcome the above-mentioned drawbacks of the prior art by providing a magnetic recording device having a novel construction based on a different principle from that for the conventional magnetic recording devices and capable of recording at a dramatically high density.
The present invention has another object to provide an electron beam recording device capable of solving the thermal agitation problem in the magnetic recording and trade-off problem related to the near-field light used in the optical recording to break through the recording density limit of the conventional peripheral storage units.
The Inventors of the present invention propose a thermally-assisted magnetic recording device based on a novel concept to attain the above object. In this thermally-assisted magnetic recording device, magnetic particles so fine that noise therefrom is sufficiently small are used and a recording layer having a high anisotropy energy density (Ku) at a temperature near the room temperature is used to assure a thermal agitation resistance. In a medium having such a large Ku value, since the magnetic field intensity necessary for recording exceeds the intensity of a magnetic field developed by the recording head when the ambient temperature is near the room temperature, no recording is possible. However, by locally heating the recording medium by any means, the coercive force Hc0 of the temperature-elevated portion of the medium can be reduced to below the magnetic field intensity of the recording head to write information to the medium.
The recording medium may be heated by irradiating light beam to near the recording magnetic pole. By locally heating the medium with the light beam during recording, the Hc0 value of the temperature-elevated portion of the medium can be reduced to below the intensity of the magnetic field developed by the recording head, thereby permitting to write information to the medium.
When a light beam from a conventional light source is used as a heat source, however, since the size of light spot is defined by the diffraction limit, an area of several hundreds of nm or more will be heated. Thus, use of such a light beam is not suitable for a future magnetic recording in which the track width will be 100 nm or less. Also, a near-field light may be used in order to limit the light beam to less than the diffraction limit. However, a near-field light emitted from a conventional light source cannot be used efficiently and the reduction in area of the temperature-elevated portion and light beam power are in a trade-off relation with each other, thus no sufficient heating can be assured in a recording at a high density.
That is, in the modality in which a far-field light is used as a heat source, the light spot size is defined by the diffraction limit, so no heating of a fine area is possible. On th other hand, the near-field light cannot be used with a high efficiency, and thus sufficient heating is difficult in a higher density of recording.
To avoid the above problem, the present invention uses an electron beam as a heat source.
Namely, the above object can be attained by providing a thermally-assisted magnetic recording device including, according to the present invention, an electron emission source of electron emitter and a magnetic recording head, electrons being directed from the electron emitter towards the magnetic recording medium to heat a recording portion of the magnetic recording medium and magnetic information being written to the temperature-elevated recording portion by the magnetic recording head applying the recording magnetic field to the magnetic recording medium. The electron beam can be limited very easily to a very fine spot size, whereby the recording density can considerably be improved.
In the above thermally-assisted magnetic recording device according to the present invention, the electron emitter can heat the magnetic recording medium so that the coercive force of the recording portion of the magnetic recording medium will be smaller than the intensity of the recording magnetic field developed at the recording portion by the magnetic recording head. Thus, positive recording is possible to a recording medium having a large coercive force.
Also in the above apparatus, the recording portion of the magnetic recording medium has a larger coercive force than the intensity of the magnetic field developed by the magnetic recording head, at the normal temperature. This magnetic recording medium is strong against the thermal agitation and the size of recording cells can be made rather smaller than the recording cell size in the conventional magnetic recording medium.
Further, in the above apparatus, there is provided a driving mechanism to move a recording surface of the magnetic recording medium in relation to the electron emitter and magnetic recording head, and after the magnetic recording medium is moved by the driving mechanism, the electron emitter will come nearer to a leading position in relation to the recording surface than the magnetic recording head. Thus, it is possible to positively elevate the temperature of the recording portion of the magnetic recording medium prior to recording.
Also in the above apparatus, the electron emitter includes a plurality of electron emitters disposed along the direction of the movement thereof by the driving mechanism. Thus, the recording portion of the magnetic recording medium can positively be heated.
Moreover in the above apparatus, there are formed on the magnetic recording medium a recording track parallel to the moving direction; the length Te of the electron emitter in the width direction of the recording track and length Tw of the magnetic recording head in the width direction of the recording track are in a relation of Te/2xe2x89xa6Twxe2x89xa62Te with each other.
Moreover in the above apparatus, the electron emitter emits electrons by field emission. Thus, fine electron beam can positively generated, and the electron emitter has an improved reliability and operating life.
Also in the above apparatus, the electron emitter is placed in a non-oxidizing atmosphere or depressurized atmosphere. Thus, the electron emitter has a further improved reliability and service life.
In the above respect, the oxygen partial pressure density X (in mols/cm3) and emission electron current density J (in A/cm2) of the electron emitter are in relations of Xxe2x89xa61.25xc3x971012xc3x97J and Jxe2x89xa6104 with each other.
In the thermally-assisted magnetic recording according to the present invention, an electron emitter is used as a heat source. The electron emitter may be any of various types such as field emission type, thermoelectronic emission type, photoemission type, tunnel electron emission type, etc. The xe2x80x9cfield emission typexe2x80x9d is such that by providing a high potential gradient (electric field) on an electron emission surface, electrons are directly emitted from the surface. The present invention adopts a field emission type electron emitter. In this case, since the electron emission area is on the order of 10 nm, an area of about 10 nm of the medium can easily be heated, thus the present invention can attain a resolution much better than that of the conventional method using the light beam. Also in case an electron emitter of the thermoelectronic emission type is used, however, the nearly same effect can be assured by converging the electron beam to a predetermined size.
Normally, the electron beam is used under a vacuum. However, taking in consideration the facts that the spacing between the magnetic head and medium is several tens of nm or less and this spacing will further be reduced in future and that the mean free path of electrons at 1 atm. is on the order of 150 nm which is sufficiently longer than the spacing between the magnetic head and medium, it can be said that emitted electron beam can be directed towards the medium with no collision. Namely, the electron emitter can be installed in a magnetic recording device which is to be used at normal atmospheric pressure.
Note that the mean free path of electrons depends upon the type of gas and electron energy. However, in case the gas used is a nitrogen being one of the major elements of air, the mean free path of electrons will be shortest even when the electron energy is 2 eV or so. The mean free path, in the nitrogen at atmospheric pressure, of the electron having the energy of 2 eV is 150 nm. Also, in case the gas used is oxygen being another major element, the mean free path of electrons is shortest when the electron energy is on the order of 20 eV. However, the mean free path is 300 nm or more, which is long enough as compared with the above-mentioned spacing.
Further, when the electron beam is used in a depressurized atmosphere according to the present invention, the probability of collision before an electron beam is incident upon the medium can be said to be rather low. Also, in case the gas used is an inert gas atmosphere according to the present invention, when it is a dry nitrogen, the mean free path of electrons is a minimum of 150 nm or so as in the above. When a rare gas such as Ne, Ar, Kr or Xe is used, the minimum value of mean free path of electrons at 1 atm. is 1000, 160, 130 or 94 nm, which is long enough as compared with the above spacing. The electrons can be incident upon the medium with little collision.
An inert gas atmosphere at a substantial atmospheric pressure should preferably be charged in the recording device for a longer service life of the electron emitter. When dry nitrogen is used as the inert gas, the mean free path of electrons is a minimum of 150 nm or so. Also when a rare gas such as Ne, Ar, Kr or Xe is used, the mean free path of electrons is long enough as in the above. In case, with the spacing between the magnetic head and medium being of several tens of nm, the electron beam can substantially work as under a vacuum. In this way, use of the dry nitrogen or rare gas atmosphere can permit a stable performance of the electron beam.
Also, the pressure of the atmosphere in which the electron beam is used may be near, higher or lower than 1 atm. However, a pressure of the atmosphere being at a substantial atmospheric pressure is convenient from the practical viewpoint.
On the assumption that the pressure inside the apparatus is P (in Torr), the minimum value of the mean free path of electrons at 1 atm. is xcexmin (in nm) and the spacing between the electron emitter and medium is d (in nm), the present invention should desirably meet the following condition:
d less than xcexminxc3x97(760/P) 
The minimum value of mean free path of electrons xcexmin is defined to a mean free path over which there will take place no collision with a probability of 1/e (e is a base of natural logarithm) when the electron travels over the distance of xcexmin. That is, when the condition d less than xcexminxc3x97(760/P) is met, the electron will collide with molecules with a probability of about 63% in the course since it is emitted until incident upon the medium. More preferably, the following condition should be met:
d less than (⅓)xc3x97xcexminxc3x97(760/P) 
When the above condition is met, the collision probability can be reduced to less than xc2xd. It is more desirable to use a coefficient of ⅕ in place of the coefficient of ⅓ in the above expression. With this coefficient, the collision probability can be reduced to so small a value as will not be inconvenient in practice.
The pressure P inside the apparatus falls within a substantial range of the atmospheric pressure. Within a range meeting the above condition, it may be selected depending upon whether a practical apparatus is feasible with the lower limit of the pressure P. If the pressure inside the apparatus is different from the atmospheric pressure or if the apparatus is charged with a gas different from the atmosphere, a hermetic enclosure is required.
In case the hermetic enclosure is used, the lower limit of the pressure P depends upon the mechanical strength of the enclosure as the case may be. In case of the conventional electron beam recording device under a vacuum, since the enclosure is applied with a pressure as high as 1 kg/cm2, it is not easy to assure a sufficient mechanical strength of the enclosure and also to maintain the vacuum state.
According to the present invention, however, the lower limit of the pressure P can be selected depending upon the practically allowable pressure to the enclosure and vacuum sealing of the enclosure. Since the lower limit of the pressure P should be considered in designing the enclosure, it cannot be fixed to a general value. However, a half or so of the atmospheric pressure may be reasonable. When the lower limit of the pressure P is higher than the half of the atmospheric pressure, the pressure applied to the enclosure will be 0.5 kg/cm2 or so and the sealed or hermetic extent of the enclosure may be a sealing provided by the ordinary aluminum sash for example.
The upper limit of the pressure P is basically defined by the above expression. The practical upper limit is double the atmospheric pressure or so based on the same consideration to the lower limit. The xe2x80x9csubstantial atmospheric pressurexe2x80x9d referred to herein is as having been described in the foregoing.
Now, the electron emitter of the field emission type will be considered. The electron emission area of this source depends in size upon the applied electric field and shape of the electron emitter. The size of the electron emission area is on the order of 10 nm when the electric field is 106 to 107 V/cm and the electron emitter has a sharpened or tapered shape obtained by a selective etching or whose end curvature is several tens of nm or less. This size is difficult to realize with a light beam and the electron emitter should preferably be applied to a future magnetic recording device in which recording cell size is several tens of nm. Emission current depends on the applied electric field. With an electric field of 106 to 107 V/cm, an emission current of about 10xe2x88x926 to 10xe2x88x924 can be obtained from an area of 10 nm in diameter.
Note that the emission current is nearly proportional to the square of the intensity of applied electric field according to the Fowler-Nordheim expression. Therefore, if the electric field intensity is 3.3xc3x97107 V/cm for example, the emission current can be 10xe2x88x923 A. Although an electric field intensity of 106 to 107 V/cm may seem to be very high, it will be suitably applicable to the magnetic recording device since the voltage to be applied between the electron emitter and medium is a maximum of several volts to several tens of V because the above spacing is several tens of nm.
Next, the mechanism of heating of the medium by electron beam will be described. When a voltage of 10 V is applied (with the spacing being 10 nm and field intensity being 107 V/cm), an emission current of 10xe2x88x924 A will provide a power of 10xe2x88x923 W. When a voltage of 33 V is applied (with the spacing being 10 nm and field intensity being 3.3xc3x97107 V/c), an emission current of 10xe2x88x923 A will provide a power of 3.3xc3x9710xe2x88x922 W. When this power is applied to a square area on the medium, whose one side is 10 nm long, the power density will be 109 W/cm2 or 3.3xc3x971010 W/cm2. When 10 m/s is used as a practical linear velocity (moving speed of the medium in the direction of the recording track) in the magnetic disc drive, the medium takes a time of 1 ns for passing by the heated area of 10 nm. Therefore, the energy density applied to the square area whose one side is 10 nm long will be 1 J/cm2 or 33 J/cm2. It will be considered herebelow whether this value is adequate for heating the medium.
As an example of the heating mechanism using an electron beam, there is available a heating mechanism in which the electron beam behaves as de Broglie wave to heat the medium. The de Broglie wave is on the order of 0.4 nm when the electron energy is 10 V while it is about 0.2 nm when the electron energy is 33 V. Namely, it is equal to the atom size, so a lattice vibration (heating) can be generated. Alternatively, there may be available a mechanism in which an electron beam having such an energy is incident upon the medium to oscillate and excite the plasmon, and an energy emitted when the plasmon-oscillated electron and positive hole in pair are recombined is given to a phonon, namely, to a lattice to induce a lattice vibration, that is, a heat.
The power density or energy density necessary for heating the medium can be considered to be nearly equal to that used with the optical disc. So, if the above power density 109 W/cm2 or 3.3xc3x971010 W/cm2, or energy density 1 J/cm2 or 33 J/cm2, is equal to or larger than the power density or energy density used with the optical disc, the medium can be heated sufficiently with the electron beam. In a common phase-change disc, for example, a linear velocity of 6 m/s, full width at half maximum (FWHM) of 0.6 xcexcm of the light spot and a recording power of 10 mW will permit to heat this medium to a higher temperature than its melting point (600xc2x0 C.). Since the medium takes a time of 100 ns for passing by the full width at half maximum and the area of the light spot is 0.28xc3x9710xe2x88x928 cm2, the power density will be 3.5xc3x97106 W/cm2 and energy density will be 0.35 J/cm2. Therefore, it can be said that the medium can sufficiently be heated by the plasmon oscillation with a energy density of 1 JIcm2.
In addition, there can take place a Joule-heating mechanism in which the electron beam causes a current to flow through the medium which is thus heated by the Joule-heating. This mechanism will coexist with the above-mentioned plasmon-oscillation heating mechanism. Comparison with the power density used with the optical disc will lead to the understanding of the reason why the Joule-heating mechanism is suitable for heating the medium. Specifically, when a current of 10xe2x88x924 A or 10xe2x88x923 A is supplied to a square area whose one side is 10 nm long of the medium in the direction of the layer thickness, the heating power will be Rxc3x9710xe2x88x928 W or Rxc3x9710xe2x88x926 W where R is a resistance of the medium. When the resistivity of a magnetic recording medium or magneto-optical recording medium is (5 to 6)xc3x9710xe2x88x926 xcexa9cm, the area of current path is 10xe2x88x9212 cm2 (10 nm square) and the current path length, namely, magnetic layer thickness is 2xc3x9710xe2x88x926 cm (20 nm), the resistance of the medium will be 10 Q or so. Therefore, the heating power will be 10xe2x88x927 W or 10xe2x88x925 W. Division of this heating power by the heated area of 10xe2x88x9212 cm2) provides 105 W/cm2 or 107 W/cm2. Since the time of current supply is different from the time of electron beam incidence, the Joule-heating mechanism should be considered by comparison in power density, not in energy density. Thus, it can be said that the current of 10xe2x88x924 A will be somewhat insufficient, but 10xe2x88x923 A will enable a sufficient Joule heating.
Actually, there will take place together, as mentioned above, the process in which the medium is heated by the plasmon oscillation and excitation and the process in which the medium is heated by the Joule heating due to the current supply to the medium. In any of the above processes, the power density and energy density are sufficient. Therefore, any of these heating mechanisms may be selected for use in the thermally-assisted magnetic recording device according to the present invention.
The thermally-assisted magnetic recording head according to the present invention should preferably be embodied as a one in which an electron emitter and recording magnetic pole are disposed in this order from the downstream (leading) side in the direction of the medium movement. Owing to this arrangement, a recording magnetic field can be applied to the medium at a position where Hc0 has become sufficiently low immediately after the medium is heated by the electron beam. The distance between the electron beam incident position and recording magnetic field-applied position depends upon the thermal response of the medium as well, but should preferably be 100 nm or less, and more preferably be several tens of nm or less.
For a higher efficiency of the heating, a plurality of electron emitters in the electron emitter should be disposed in the direction of the recording track. The size of the heated area should preferably be nearly equal to the width of the recording track to enable a uniformmagnetic transition over the trackwidth. Also the track width Te of the electron emitter, and track width Tw of the recording head should desirably meet the condition of Te/2xe2x89xa6Twxe2x89xa62Te.
The inside of the ordinary magnetic disc drive communicates with the ambient atmosphere. When the electron beam is to be used in an atmosphere containing oxygen and moisture, consideration should be given to the life of the electron emitter as well as to the mean free path of electrons. At atmospheric pressure, air molecules or water molecules in the atmosphere will be adsorbed by the electron emitter and will possibly shorten the service light of the latter. Different from the conventional thermal emission type electron beam emitter and photo emission type electron beam emitter, the field emission type electron beam emitter having actively been researched and developed recently is extremely resistant against adsorbed molecules. When carbon (C) is used as a material for the electron emitter, the latter will be less influenced by the oxidation. For a practically long service life of the electron emitter, however, the densities of the gas atmosphere near the emitters, especially, the densities of oxygen, water and their dissociated species, and the frequency of their incidence upon the emitters, should be kept low.
The Inventors of the present invention made many experiments mainly on STM (scanning tunneling microscopy) emitter, and found from the experiment result a emitter-surrounding atmosphere required for obtaining a field emission current stably. As will further be described later concerning the embodiments of the present invention, the Inventor of the present invention found that it depends upon the emitter material how the emitter-surrounding atmosphere should be and that also when silicon (Si) on which a surface oxide film is easy to develop was used, electrons could be emitted stably if the density X (mols/cm3) of oxygen molecules in the emitter-surrounding atmosphere and current density J (in A/cm2) of electrons emitted from the emitter met the condition of Xxe2x89xa61.25xc3x971012xc3x97J with Jxe2x89xa7104. The definition of the range of J as in the above condition is intended to present a necessary range of J for significantly heating the medium. There will be no sense in defining an emission current with which no significant heating will take place or a relation between X and J which would be when the emitter stops operating.
When the emitter stops operating, a natural oxide layer or a physical adsorption layer will develop on the emitter surface. When the above defined condition in the present invention is met, such layers will easily desorb the emitter surface due to the following operation of the emitter. The above definition of the relation between X and J in the present invention is intended to present a condition under which so long as an emission current capable of significantly heating the medium is supplied, the tip of the emitter will not be deteriorated due to attack by oxygen. The relation between X and J has a physical meaning that while a hundred electrons are being emitted from the emitter, one oxygen molecule will be incident upon the emitter surface. With such an extent of the incidence of oxygen molecule, heating of the emitter surface by the electron emission, etc. will allow the incident oxygen to re-desorb the emitter surface which will thus not be deteriorated, which is one of the findings of the above Inventors"" experiments.
As having been described in the foregoing, according to the present invention, a low-noise multiparticle medium formed from very fine particles, necessary for a high density magnetic write and read, can be made to have a sufficiently high resistance against the thermal agitation at a temperature near the room temperature, and the coercive force of the medium, that is, a necessary magnetic field for a magnetic transition, is reduced by incidence of an electron beam upon a portion of the medium to which a recording magnetic field is applied, to thereby enabling a practical recording head to attain a high speed of recording.
Also, according to the present invention, an electron emitter and write and read elements are formed integrally with each other to provide a compact and lightweight thermally-assisted magnetic recording head, which will enable a high speed seek operation and inexpensive head and drive.
Further, according to the present invention, it is possible to improve to a practical level the service life of the electron emitter of a thermally-assisted magnetic recording device in which a medium is heated by a high resolution, high efficiency electron emitter, the coercive force of the heated portion of the medium is reduced and a recording magnetic field is applied to the portion whose coercive force has thus been reduced, thereby recording information to the medium.
On the other hand, according to the present invention, a magnetic pole or magnetic yoke can also be used as an electron emitter, thereby enabling a magnetic write and read with a further high recording density.
Also according to the present invention, an electron emitter having an extremely superior recording resolution to that of the light beam or magnetic recording head used in the conventional magnetic recording device, can be used to write information to a medium. Thus, according to the present invention, there can provided a practical magnetic recording device in which information can be recorded with a considerably improved density and an electron beam recording can be done in the atmosphere, which is impossible with the conventional electron beam recording.
That is, according to the present invention, there can be provided a thermally-assisted magnetic recording device realizing a new concept that information can be recorded with a drastically higher density than with the conventional recording device. Thus the present invention is very advantageous in the field of art.
These objects and other objects, features, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments of the present invention when taken in conjunction with the accompanying drawings. It should be noted that the present invention is not limited to the embodiments but can freely be modified without departing from the scope and spirit thereof defined in the claims given later.